The present invention relates to an information reading apparatus, and more specifically to an optical information reading apparatus.
With the remarkable development of the information industry, information recording or reproducing (reading) apparatuses for recording or reproducing a variety of types of information have recently been put to practical use. Apparatuses have conventionally been proposed which record or reproduce information magnetically. The apparatuses of this type cannot, however, ensure prolonged retention of recorded information, making high-density recording difficult.
An apparatus for optically reproducing information is disclosed in U.S. Pat. No. 4,360,728. This apparatus comprises a condensing lens for converging light emitted from a laser beam source, and a pair of mirrors for reflecting the converged light to project it onto a card which bears information. The light applied to the card is reflected with a reflectivity which varies with the presence of pits or recorded data on the card. The reflected light is deflected by a half mirror, and then focused on a photodetector, such as a photodiode, by a focusing lens. Thus, the recorded data on the card is read or reproduced optically. For optical scanning of a recording region on the card, the paired mirrors are oscillated synchronously.
In the apparatus of the aforementioned construction, the optical system needs to be arranged in three dimensions, making the apparatus bulky as a whole and requiring a troublesome positional adjustment between members. Also, to permit oscillation of the mirrors requires complicated construction and expensive manufacturing.
Therefore, the inventor hereof has proposed a record information reading apparatus which employs a plane optical waveguide, in Japanese Patent Disclosure No. 53-13819. This apparatus comprises a grating for leading a light beam emitted from a light source to the waveguide, and an ultrasonic vibrator for producing a surface elastic wave region in the optical path of the beam. Part of the beam passing through the elastic wave region is refracted and converged on an end face of the waveguide by a converging lens. The angle of refraction of the light beam refracted by the elastic wave region is continuously changed by applying an AC signal voltage to the vibrator to vary the frequency of surface elastic waves in succession. Thus, the beam converged on the end face of the waveguide is shifted for primary scanning in a predetermined direction.
According to the apparatus described above, the optical system can enjoy a substantially plane configuration, and mirrors, unlike the ones employed in the aforementioned conventional apparatus, need not be mechanically oscillated. Accordingly, the whole structure of the apparatus can be made compact, the number of adjustments can be decreased, and the manufacturing cost can be reduced. In the apparatus of this type, however, synchronizing signals for determining the timing for the primary scanning are generated by an encoder which, mounted on a rotating body, would constitute a hindrance to further reduction in the size and cost of the apparatus.